var a = 10;

In programming, to hold values, we use variables. How do we declare variables in Javascript? We declare them using the word var.

a is the name of the variable. a is like a box containing the value 10

= is the equality operator.  What is an operator? It is character that represents an action. That action can be performed on values and variables. Other operators are +,- , * ..etc

10 is  the value.

Dynamic Typing

Static Typing

• Some programming languages declare variables to hold a specific type of data.
• it prevents unintended value conversions
• examples of static programming languages: C, C++
•  

int x = 0;

Javascript provides a typeof operator that examines a value of a variable and tells you what type it is

var x ;
console.log(typeof(x));

// it can be used as typeof x;

x = 2;
console.log(typeof(x));

x = 3.4;
console.log(typeof(x));

var school = 'Galvanize';

console.log(school[0]); // G

• var firstName = 'Bella';
• var someName = 'Bella ';

these two values are not the same. 

'Bella' has a length of 5 while 'Bella ' has a length of 6. 

Spaces count

length is a property of a string.

It counts the number of elements or characters in a string.

var name = 'My name is bond';

console.log(name.length);

Find the length of the following strings

var t = 'James';

var y = '  ';

var x = ' ';

hint: use console.log() to print the length to the console.

Google mdn javascript String

• Create  a variable to hold your name
• make all the letters upper-case using a method
• make all letters lower case using a method

var b = true;

var c = false;

a boolean value is another way of representing a yes or no answer, or 0 or 1. 

when a variable doesn't have a value assigned , the type of the data in that case is undefined.

var y ;

console.log(typeof y);

var a = null;

typeof null // 'object'

this is a bug in javascript

null is when variable doesn't have a value.

It is not my fault. javascript was created in 10 days ..

Null

a variable doesn't have a value. 

Undefined

variable doesn't have a type. 

var x;

a = "hello world";

b = 42;

c = true;

d = null;

e = undefined;

determine the data type of the following variables

use typeof

var obj = {
    a: 1.47,
    b: 1,
    c: true,
    d: 'Hello World'
};

example

How can you access the object properties? 

Can you modify their values? 

How can you add properties to the object?

You can access the object properties using three ways:

Dot Format

obj.b;

var obj = {
    a: 1.47,
    b: 1,
    c: true,
    d: 'Hello World'
};

bracket notation

obj['b'];

variables

var x = 'b';

obj[x];

create an object named person, add keys to store your first name, last name, age, 

var person = {};

person.firstName = 'Halah';
person.lastName = 'Al-Shaikhly';
person.age = 26;

console.log(person);

var arr = [];

// this is how you declare an empty array

var arr = [
    "hello world",
    42,
    true,
    {a :1, b:'yo'}
];


console.log(arr);

arr[0]; // accessing index zero
arr[1]; // accessing index 1

arr.length; // what is length?

typeof arr; // what is the result of this?

make an array named dogs, it has 3 items. Each item is a dog and each dog has a name, age and  whether or not they like cats.  

Print the last dog's age. 

Hints

• each dog might be an object ..
• that object might have properties .. 
• liking   a cat property could be of type boolean .. 

"a function is composed of a sequence of statements called the function body. Values can be passed to a function, and the function will return a value."

function functionName(param1,params2 , ....){
    //statements
}

function

it is the key word to declare a function

functionName

this could be f1, anything that is not a reserved word

params

values passed to the function

statements

any statement

How to declare a function

// function being declared
function myFunction(){
}

// how to call a function

myFunction();

function myFunction2(){
}

console.log(myFunction2());

function myFunction3(){
    
return 1;
}

console.log(myFunction3());

How to can I pass data to a function?

function f1(x){
    console.log(x*x);
}

f1(3);
//pass multiple data
function f2(x, y){
    
    console.log(x*y);
}

f2(3,5);
//what happens if I send one value only? 
f2(3);

//let's try a return statement
function f3(x){
    return x *3;
}

console.log(f3(4));

How to can I pass data to a function?

function f7(x){
    console.log(x*x);
}

// what will be the result here? why?
console.log(x);

var y = 8;
function f8(){
	y = 9;

}
// what is the output of this? 
console.log(y);
//how about now, why?
f8();
console.log(y);

Can I pass other datatypes to a function?

what other datatypes I can pass?

can I pass a function to another function as parameter?

Can a variable hold a function?

What's an anonymous function?

//takes an array as a funcion argument
function printData(data){
	console.log(data);
}
//passing an array
printData([1,2,3]);
//passing an object
printData({
	a:1,
	b:2
});

function sum(x,y){
	return x +y;
}

//passing a function
printData(sum(1,2));

// anon function is a function without a name
var p = function(){
	console.log('I have no name. I\'m an anon function');
	return 4;
}

function h(f){
	console.log('im inside h');
	console.log(f());
}

h(p);

 They tell JS which statements to execute, based on a condition.

// syntax
if (condition){
// statements to be executed.
}

//example

var b = 23;

if (b > 20) {// evaluates to true
    console.log('condition is met');
}

if(b > 20 && b <= 23){
    console.log('b is between 20 and 23');
}

if you're not using equality, comparison or logical operators in a condition, then javascript tries to determine whether this condition/value is truthy or falsey.  

Truthy value is everything else. All values are truthy unless they're defined as falsey.

Falsey value is a value translated to false when evaluated in a boolean context. 

everything else is a truth value.

if the condition(s) in the if statements are not met, execute other statements

var b = 10;

if(b < 5){
    console.log('b is less than 5');
}
else{
    console.log('b is greater than 5');

}

for multiple conditions

var b = 5;

if(b < 5){
    console.log('b is less than 5');
}
else if(b > 5){
    console.log('b is greater than 5');

}
else{
      console.log('b equals 5');
}

declare two variables, give them values of your own choice and write some statements to determine if one the values is greater than or equal the other value.  Print the result to your console.

Hints

• use console.log to print results
• use if/else if/else

var x = 40;

var y = 89;

if( x > y){
    console.log('x is greater than  y')
}
 else if(x < y) {
    console.log(' y is greater');
}

else{
    console.log('x and y are equal');
}

Loops are a way to do something repeatedly

all loops repeat the same action several times.

• For loops
• do while loops
• while loops
• for in loops

for(var i = 0; i < 5; i++){

    console.log('I\'m a statment running for i= '+ i);
}

use the keyword for to start a for loop

initial expression

the condition. this where you determine how many times the action is repeated

incremental expression

Statement or action to be repeated till condition is false

Halah Al-Shaikhly

@twiter: halinaSalih

@email:halah.alshaikhly@gmail.com

@github:halahRaadSalih